MACH2 Simulations of Exothermic Propellants in a Micro-laser Ablation Plasma Thruster (original) (raw)
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Computer Simulations of Exothermic Propellants in a Microlaser Ablation Plasma Thruster
2012
Interest in development of micro- and nanosatellites has led to the design of the microlaser ablation plasma thruster. Previous work succeeded in constructing a working computational model of the microthruster’s operation via MACH2, a two-dimensional magnetohydrodynamic code; however, this model was limited to simulating only nonenergetic solid propellant ablation in the microthruster. Recent experimental investigations have demonstrated that use of an exothermic (energetic) propellant can significantly improve performance of the microthruster and allow for higher-thrust modes of operation. The present work details new simulations of exothermic glycidyl azide subdetonation and full detonation processes; the results indicate a successful capability to match the detonation characteristics of the glycidyl azide and its ablative behavior. Particularly, the threshold for the onset of detonation in the fuel is explored and matches within approximately 14% of theoretical calculations of threshold pressure. This demonstrates the possibility to explore the selection of fuel for the microlaser ablation plasma thruster via computational investigations. Glycidyl azide polymer subdetonation simulations indicate a 74% improvement in impulse bit over the previous nonenergetic propellant. A confined ablation setup is also explored for detonation, which demonstrates a vast improvement to performance while suppressing the propagation of shocks.
MACH2 Simulations of a Micro-laser Ablation Plasma Thruster with Nozzles
Recent work has investigated the micro-laser ablation plasma thruster (μLPT), a sub-kilogram form of satellite propulsion. Computational simulations that simulate the operation of the micro-thruster using the magnetohydrodynamic code MACH2 have already been established. The investigations made here have extended the capabilities of the previous computational model and have been applied to a new micro-thruster operation design incorporating a conical nozzle to demonstrate enhanced thruster performance. A methodology is presented that was developed in the MACH2 code that allows for the calculation of performance parameters characterizing the micro-thruster operation mode, such as coupling coefficient and specific impulse. The presence of a nozzle is shown to improve the coupling coefficient by as much as 36% and the specific impulse by as much as 50%, and the resulting nozzle performance enhancement follows typical nozzle trends realized in thermal rockets.
Plasma generation and plume expansion for a transmission-mode microlaser ablation plasma thruster
Journal of Applied Physics, 2004
An end-to-end model is presented of the transient plume created by a microlaser ablation plasma thruster. In this article, we describe a model of the plasma generation and expansion for a micro-laser plasma thruster operated in transmission-mode ͑T-mode͒. The laser ablation and plasma formation processes are modeled using a kinetic ablation model. This procedure provides boundary conditions at the target surface for the plume model that is based on a particle computational approach. The present study considers a 2.5-8 W diode-based laser irradiating a poly-vinyl chloride target for a pulse length of 3-10 ms. Laser beam shape full width at half maximum at the target is about 25ϫ25 m. The plume simulations reveal many details of the multicomponent plasma expansion. The results are compared with experimentally obtained plume signatures. Generally good agreement between experimental and calculated flux profiles is found.
Proceedings of SPIE, 2004
The micro laser plasma thruster (tLPT) is a micropropulsion device, designed for the steering and propelling of small satellites (10 to 100 kg). A diode laser is focused on a two-layer polymer tape, where it forms a plasma. The thrust produced by this plasma is used to control the satellite motion. Three different polymers (GAP, PVN and PVC) doped with carbon and/or IR-dye were investigated for their performance as fuel polymer. The different dopants for GAP seem to have only little influence in the ablation properties. The most pronounced differences are observed in the fragment ejection detected in the shadowgraphy measurements and the crater appearance. For all carbon doped polymers, the ablation spots have a similar rough morphology. The shadowgraphy measurements of PVN reveal, that the shockwave and particle plume propagates faster as in the case of the other polymers. The particle plumes showed a very different expansion behavior for all polymers, whereas the plasma temperature and electron density measurements showed no significant difference. Only PVC displayed a slower almost liner drop of the plasma temperature over time. The thrust measurements showed the best results for GAP. *
Micropropulsion using laser ablation
Applied Physics A, 2004
The micro-laser plasma thruster (µLPT) is a new micropropulsion device that uses laser ablation to create very small thrusts (0.1-100 µN) for pointing and positioning microand nano-satellites. In this paper, we discuss the expected performance of the µLPT. For a ms-pulse device, target materials are restricted to those of low thermal conductivity, e.g. polymers. Volume ablation theory adequately describes their behavior. In a ns-pulse version, exhaust velocity can be an order of magnitude higher with correspondingly lower thrust-to-power ratio. The theory for surface absorbers describes the observed behavior.
A Review of Laser Ablation Propulsion
Laser Ablation Propulsion is a broad field with a wide range of applications. We review the 30-year history of laser ablation propulsion from the transition from earlier pure photon propulsion concepts of Oberth and Sänger through Kantrowitz's original laser ablation propulsion idea to the development of air-breathing "Lightcraft" and advanced spacecraft propulsion engines. The polymers POM and GAP have played an important rôle in experiments and liquid ablation fuels show great promise. Some applications use a laser system which is distant from the propelled object, for example, on another spacecraft, the Earth or a planet. Others use a laser that is part of the spacecraft propulsion system on the spacecraft. Propulsion is produced when an intense laser beam strikes a condensed matter surface and produces a vapor or plasma jet. The advantages of this idea are that exhaust velocity of the propulsion engine covers a broader range than is available from chemistry, that it can be varied to meet the instantaneous demands of the particular mission, and that practical realizations give lower mass and greater simplicity for a payload delivery system. We review the underlying theory, buttressed by extensive experimental data. The primary problem in laser space propulsion theory has been the absence of a way to predict thrust and specific impulse over the transition from the vapor to the plasma regimes. We briefly discuss a method for combining two new vapor regime treatments with plasma regime theory, giving a smooth transition from one regime to the other. We conclude with a section on future directions.
Optimization Issues for a Micropulsed Plasma Thruster
Journal of Propulsion and Power, 2006
In this work we consider several issues related to design of a micro-Pulsed Plasma Thruster (µ µPPT). One example of such a device has been developed at the Air Force Research Laboratory for delivery of a very small impulse bit. It is concluded that the choice of the optimal energy level for a given micro-PPT geometry is very important. If discharge energy is small, the so called propellant charring would limit the operational time of the thruster. It is found that the charring phenomenon is associated with non-uniformity (in the radial direction between the electrodes) in the propellant ablation rate. On the other hand higher energy leads to discharge constriction on the positive electrode and causes azimuthal non-uniformity. Reasoning leading to such non-uniformity is considered and recommendations for optimal energy and thruster size selections are presented.
Review: Laser-Ablation Propulsion
Laboratory for two years and, since 1974, as a Senior Research Staff Member in the Advanced Optical Systems Group at Los Alamos (LANL). There, he conducted a research program on mechanical and thermal coupling of pulsed lasers to targets using high-energy-laser facilities in the United States and United Kingdom, and he developed a model for vacuum laser impulse prediction. From 1994 to 1995, he was Associate Director of the Alliance for Photonic Technology at LANL. In 1995, he formed Photonic Associates, which is devoted to applications of laser space propulsion. He is the author of 110 papers and 40 invited talks and an editor of a book on laser ablation, and he has been the organizer and chair of seven symposia on high-power laser ablation. He is a Governing Board Member of the American Institute of Beamed Energy Propulsion, which gave him its lifetime achievement award in 2005. He is a Senior Member of the AIAA.
Polymer ablation: From fundamentals of polymer design to laser plasma thruster
Applied Surface Science, 2007
UV-Laser ablation of polymers is a well-established method to structure and deposit polymers, but the mechanisms of ablation are still controversial, i.e. photothermal or photochemical processes. An approach to probe the ablation mechanisms and to improve ablation is to incorporate photoactive groups into the polymer structure. The investigation of the ablation behavior of designed triazene polymers showed that the ablation mechanism is always a combination of both photothermal and photochemical processes, but the ratio can be changed by using different polymers and irradiation wavelengths. Also the quality of structures in the triazene polymers is superior at an irradiation wavelength of 308 nm compared to commercially available polymers. Polymers can be designed not only for UV irradiation, but also for applications in the IR range, but with different requirements. One application for designed polymers in the near-IR range is as fuel for the laser plasma thruster, which is used as propulsion system for small satellites. With commercially available polymers the necessary thrust could not be achieved. A specially designed polymer-absorber system for this application produce more energy in the form of thrust, than the laser delivered.
Diode laser-driven microthrusters - a new departure for micropropulsion
AIAA Journal, 2002
We developed an entirely new type of orientation thruster for micro-and nanosatellites. The laser plasma thruster is based on the recent commercial availability of diode lasers with sufficient brightness and 100% duty cycle to produce a repetitively pulsed or continuous vapor or plasma jet on a surface in vacuum. A low-voltage semiconductor switch can drive the laser. A lens focuses the laser diode output on the ablation target, producing a miniature jet that provides the thrust. Single-impulse dynamic range is nearly five orders of magnitude, and the minimum impulse bit is 1 nN/s in a 100-µs pulse. Even with diffraction-limited focusing optics, at least 0.5-W optical power is needed to produce thrust from selected ablator materials. Thrust-to-power ratio C m is 50 to 100 µN/W and specific impulse I sp is 200-500 s with a 1-W laser, depending partially on the illumination mode. Transmission and reflection (R) illumination modes are discussed. R mode gives about 50% better I sp and two times better C m. Improved results are anticipated from higher laser power in the reflection mode. The prototype engine we are developing is intended to provide lifetime on-orbit steering for a 5-kg satellite, as well as reentering it from low Earth orbit.